Console Logging Functions

FireBug makes a console object available to all web pages. This object has the following functions:

Basic Logging

console.log("message" [,objects]) - Logs a string to the console. The string may contain any of the patterns described below in the "String Formatting" section. The objects passed after the string will be substituted for each of the patterns in the string in order.

Logging Levels

It is often useful to separate messages according to different levels of severity. There are four different functions for this purpose. In addition to the visual separation, these functions are also different from log in that they automatically include a link to the line number in the source where they are called.

console.debug("message" [,objects]) - Logs a debug message.

console.info("message" [,objects]) - Logs an informative message.

console.warn("message" [,objects]) - Logs a warning.

console.error("message" [,objects]) - Logs an error.

Assertions

Assertions are a great way to enforce rules in your code. The console object includes a set a common types of assertion functions, and also allows you to write your own.

console.assert(a, "message" [,objects]) - Asserts that an a is true.

console.assertEquals(a, b, "message" [,objects]) - Asserts that a is equal to b.

console.assertNotEquals(a, b, "message" [,objects]) - Asserts that a is not equal to b.

console.assertGreater(a, b, "message" [,objects]) - Asserts that a is greater than b.

console.assertNotGreater(a, b, "message" [,objects]) - Asserts that a is not greater than b.

console.assertLess(a, b, "message" [,objects]) - Asserts that a is less than b.

console.assertNotLess(a, b, "message" [,objects]) - Asserts that a is not less than b.

console.assertContains(a, b, "message" [,objects]) - Asserts that a is in the array b.

console.assertNotContains(a, b, "message" [,objects]) - Asserts that a is not in the array b.

console.assertTrue(a, "message" [,objects]) - Asserts that a is equal to true.

console.assertFalse(a, "message" [,objects]) - Asserts that a is equal to false.

console.assertNull(a, "message" [,objects]) - Asserts that a is equal to null.

console.assertNotNull(a, "message" [,objects]) - Asserts that a is not equal to null.

console.assertUndefined(a, "message" [,objects]) - Asserts that a is equal to undefined.

console.assertNotUndefined(a, "message" [,objects]) - Asserts that a is not equal to undefined.

console.assertInstanceOf(a, b, "message" [,objects]) - Asserts that a is an instance of type b.

console.assertNotInstanceOf(a, b, "message" [,objects]) - Asserts that a is not an instance of type b.

console.assertTypeOf(a, b, "message" [,objects]) - Asserts that the type of a is equal to the string b.

console.assertNotTypeOf(a, b, "message" [,objects]) - Asserts that the type of a is not equal to the string b.

Measurement

The following functions allow you to measure certain aspects of your code.

console.trace() - Logs a stack trace showing the point of execution where this is called.

console.time("name") - Begins a timer and gives it a unique name.

console.timeEnd("name") - Stops the timer with the given name and logs the number of milliseconds that have ellapsed since it was started.

console.count("name") - Logs the number of times that the line of code where this is called has been executed.

String Formatting

All of the console logging functions can format a string with any of the following patterns:

%s - Formats the object as a string.

%d, %i, %l, %f - Formats the object as a number.

%o - Formats the object as a hyperlink to the inspector.

%1.o, %2.0, etc.. - Formats the object as an interactive table of its properties.